1. Field of the Invention
The present invention relates to the field of load-bearing hydraulics, and in particular to a method and apparatus for safety protection control of temporary roof support.
2. Background Art
In mining operations, roof fall situations are of pressing concern. Safety precautions are taken to prevent personnel being injured by roof falls, including adding support structures to the roof bolter equipment. However, prior art methods of adding structural support remain dangerous for those installing the support. This problem can be better understood with a review of temporary roof supports.
Temporary Roof Supports
A temporary roof support is used to support the roof of an excavated location during installation of permanent roof support (e.g., operation of roof bolters). In one common arrangement, a dual boom roof bolter has two operators and two sets of controls for installing roof bolts. Typically, each operator is responsible for bolting one half of an entry way. Frequently, one operator also has controls on the boom to lower and raise a temporary roof support as well as to move the machine at a reduced rate of speed. Such controls are used in repositioning the machine after each row of bolts across an entry is installed.
However, under certain roof conditions, the roof may fracture while temporary roof support is supporting the roof. An operator may or may not be aware that such a fracture has occurred. During typical operation of roof bolters, the roof bolts are installed at approximately four foot intervals. Thus a large amount of rock may be broken loose between installed roof bolts and be supported solely by the temporary roof support.
Loose rock causes at least three potential hazards. First, the controls of the temporary roof support are located near the front of the roof bolter. Thus, an operator is exposed to falling rock when the temporary roof support is released. Second, a temporary roof support is supported by hydraulic cylinders with load holding valves. The speed of the decent of the temporary roof support is dependent only upon the load applied and the restrictions in the hydraulic circuit. Thus, the temporary roof support may descend at a rate that is hazardous to the operator, even though the loose rock is not free-falling. Additionally, the strain on the hydraulic circuit resulting from the rapid decent may cause damage to the temporary roof support.